Porous plug assembly for metallurgical receptacle



Sept. 26, 1967 3,343,829

POROUS PLUG ASSEMBLY FOR METALLURGICAL RECEPTACLE R. B. COATES 2 Sheets-Sheet 1 Filed March 15, 1965 p 26, 1967 R. B. coATEs 3,343,829

POROUS PLUG ASSEMBLY FOR METALLURGICAL RECEPTACLE Filed March 15, 1965 2 Sheets-Sheet 2 HHHHHIHI United States Patent 3,343,829 POROUS PLUG ASSEMBLY FOR METALLURGICAL RECEPTACLE Roderick B. Coates, Blackwell, Bromsgrove, England, assignor to The British Cast Iron Research Association, Birmingham, England, a British company Filed Mar. 15, 1965, Ser. No. 439,786 Claims priority, application Great Britain, Mar. 14, 1964,

10,892/ 64 7 Claims. (Cl. 266-39) ABSTRACT OF THE DISCLOSURE A tapered porous plug fitted in the refractory lining of a vessel for molten metal is made easily removable from outside the vessel by making it wholly of refractory material so that, although it wedges into the tapered recess in the refractory lining, it does not become fused into it but can be withdrawn. The refractory lining may have a bush in its wall in which the recess is formed and the plug can comprise an inner gas-permeable portion and an outer non-permeable shell, both being refractory.

Detailed description This invention relates to the treatment of molten metals by mixing or agitation by gas introduced into the metal through a gas-permeable plug set below the metal surface of a ladle or other container. The techniques of treating molten metals by this method are well known and have been employed for the removal of unwanted gases such as hydrogen from the molten metal and for the addition of other gases such as nitrogen where required by bubbling the appropriate mixture of gases through the gas-permeable plug.

In the past gas-permeable plugs have been used in the bottom of refractory lined ladles to only a limited extent because of the practical difiiculties of removal and replacement of plugs. Plugs of this type have a much shorter working life than the refractory lining of the ladles but with known designs plug removal has usually necessitated damage to or complete removal of the refractory ladle bottom also.

It is true that it has been proposed to make such plugs removable but hitherto not only has this still necessitated emptying the ladle or other container but it has also required that one should wait until the container has cooled down to room temperature because the plug has been found to adhere to the refractory lining of the container and consequently to damage the lining on removal, so that the lining has required patching after the new plug has been inserted.

It is an aim of the present invention to provide a gaspermeable plug assembly that allows the plug to be truly removable and replaceable without damage to the refractory lining and, if necessary, without even having to wait for the ladle or other container to cool down.

According to the invention there is now proposed a refractory-lined container for molten metal, such as a ladle, provided with a gas-permeable plug disposed in a wall of the container for the introduction of a gas into the metal, in which the wall of the container is provided with a hollow bush embedded in the refractory lining made separately therefrom, and in which the plug is a tight fit in this bush, but removable therefrom from outside the container and without disturbing the refractory lining.

The invention is applicable primarily to ladles for cast iron, in which a de-gassing operation is to be performed on the molten iron while it is in the ladle. However the invention may also be applied to holding furnaces or other containers, and to containers for metals other than lIOll.

According to a feature of the invention the bush is of hollow truncated conical form and is embedded in the lining with its smaller end flush with the inner surface of the lining.

According to a further feature of the invention the plug is not uniformly permeable to gas but is constructed in two concentric parts comprising an outer non-permeable shell, of which the outer surface matches the inner surface of the bush, and an inner gas-permeable core.

The invention will now be further described by way of example with reference to the accompanying drawin gs, in which:

FIGURE 1 is a section through a portion of the bottom of a ladle for molten iron, provided with a plug assembly according to the invention; and

FIGURE 2 shows a device for facilitating removal of the plug.

Referring first to FIGURE 1, the ladle shown is made of steel plate '1 and has a refractory lining 2 in a wellknown manner. Set in this refractory lining at a suitable point in the bottom of the ladle we provide a hollow bush 3 of truncated conical shape, set with its smaller end uppermost and flush with the upper surface of the lining 2. The length of the bush is substantially equal to the thickness of the lining and in the example shown the bush is made of a proprietary clay graphite refractory material known as Salamander. In the example illustrated the final shape of the bush is obtained by machining an extruded fired section of the material, but it could be made by another method, such as moulding.

The plug comprises an outer non-permeable shell portion 4 and inner gas-permeable portion 5. The outer portion has an external taper that exactly matches the taper on the inside of the bush 3, and it has a flange 6 at its lower end. This outer portion is made of the same clay graphite material as the bush 3. The inner portion 5 is almost cylindrical in shape, but with a very slight taper and it is made for example of olivine sand containing four percent of sodium silicate, hand-rammed into the outer portion 4 and hardened by drying at 200 C. overnight. The length of the plug is such that its smaller end is substantially flush with the end of the bush 3.

The flange 6 of the plug seats against a gasket 7 in a counterbore in a disc-like base plate 8 which in its turn seats against the underside of the ladle with the interposition of a gasket in the form of an asbestos pad 9. The base plate has an aperture aligned with the aperture in the wall 1 of the ladle and is held against that wall by wedges engaging pins which are screwed into bushes in the wall. There can be three such pins, symmetrically distributed, and one of them is visible at 10 in FIGURE 1, with its associated bush 11 and its wedge 12.

The base plate 8 likewise has three studs symetrically spaced around it, two of these being visible at 13 and 14. These receive wedges, of which one is visible at 15, to hold in place a clamping plate 16 by which the plug is held in place. It bears against the plug through the medium of a gasket 17, and presses the plug into tight sealing engagement with the base plate 8 and with conical bore of the bush 3, so that there is no possibility of the molten iron in the ladle penetrating between the plug and the bush and leading to the destruction of their mating surfaces or their becoming keyed together. On the contrary, it is found that, on release of the clamping plate 16 the plug can be withdrawn without damage to the surface of the bush 3 or the refractory lining 2 and a new plug can be inserted immediately, even in very hot conditions, and is ready for use as soon as the clamping plate is wedged in place again.

The gas with which the molten metal is to be treated is admitted through a passage '18 in the clamping plate 16, the outer end of this passage being provided with screwed connection 19. The gas passes upwards through the permeable central portion of the plug and into the metal.

Although the conical surface of the plug is free of any metal coating that might melt and adhere to the inner surface of the bush 3, there is still the possibility that the plug may become wedged in the bush during service and so we provide a special plug extractor tool, shown in FIGURE 2. It comprises a flat spider having a number of equally spaced arms 20, from each of which extends a leg 21 in a direction approximately parallel to plane of the arms. A central bore 22 receives a stout bolt 23 having its head on the opposite side of the spider from the legs and carrying a releasing nut 24 which, in the example shown, is provided with handles 25 by which it can be turned without the use of a spanner. A second nut 26 prevents the bolt falling out of the spider.

To pull out the plug the end of the bolt 23 is screwed into a nut 27 (FIGURE 1) welded to the centre of the clamping plate 16, and then, with the legs 21 hearing against the underside of the ladle, and after removal of the wedges 12, the nut 24 is turned to force the whole assembly comprising the clamping plate, base plate and plug away from the ladle.

Although olivine sand is used for the gas-permeable central section 5 of the plug in the example described, other materials are possible. For example, plugs have been made and successfully used with silica sand, zircon sand and with granular silicon carbide, bonded in each case with sodium silicate or other suitable materials, such as permeable clay-graphite or carbon. With the olivine sand central section, the life of the plug under typical conditions is around fifteen metal treatments.

I claim:

1. In a refractory-lined container for molten metal, of the type having a gas-permeable plug disposed in a wall of the container for the introduction of a gas into the metal, the improvement which comprises a plug having a frusto-conical body of refractory material and includipg an axial porous centre portion, a frusto-conical recess extending through the refractory lining of said container with its smaller end innermost, said container wall having an opening therein aligned with said recess, said plug being insertable in said recess from outside said container, the mating surfaces of said plug and of said recess both being of refractory material, and releasable retaining means serving to retain said plug in said recess.

2. The invention set forth in claim 1, including a bushing of refractory material, said recess being formed in said bushing and said bushing being embedded in the remainder of the refractory lining of said container.

3. The invention set forth in claim 2 wherein said bushing is made of clay graphite material.

4. The invention set forth in claim 1 wherein said frusto-conical body forming said plug comprises two concentric parts namely, a first part comprising an outer non-permeable refractory shell and an inner gas-permeable core.

5. The invention set forth in claim 4 wherein said inner core is made of olivine sand.

6. The invention set forth in claim 4 wherein said outer shell is of clay graphite material.

7. A tapered frusto-conical gas-permeable plug for insertion in a frusto-conical hole in a wall of a refractory lined container for the admission of gas into molten metal in the container, said plug comprising an outer nonpermeable shell of refractory material having a smooth tapered frusto-conical external surface for removable engagement in said frusto-conical hole in said container wall and an inner gas-permeable core of refractory material rem ovably received in said shell.

References Cited UNITED STATES PATENTS 2,811,346 10/1957 Spire. 2,947,527 8/1960 Spire 266-34 FOREIGN PATENTS 684,048 12/ 1952 Great Britain. 760,561 10/1956 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

7. A TAPERED FURSTO-CONICAL GAS-PERMEABLE PLUG FOR INSERTION IN A FRUSTO-CONICAL HOLE IN A WALL OF A REFRACTORY LINED CONTAINER FOR THE ADMISSION OF GAS INTO MOLTEN METAL IN THE CONTAINER, SAID PLUG COMPRISING AN OUTER NONPERMEABLE SHELL OR REFRACTORY MATERIAL HAVING A SMOOTH TAPERED FRUSTO-CONICAL EXTERNAL SURFACE FOR REMOVABLE ENGAGEMENT IN SAID FRUSTO-CONICAL HOLE IN SAID CONTAINER WALL AND AN INNER GAS-PERMEABLE CORE OF REFRACTORY MATERIAL REMOVABLY RECEIVED IN SAIDS SHELL. 